U.S. patent number 6,590,647 [Application Number 09/848,892] was granted by the patent office on 2003-07-08 for physical property determination using surface enhanced raman emissions.
This patent grant is currently assigned to Schlumberger Technology Corporation. Invention is credited to Kenneth E. Stephenson.
United States Patent |
6,590,647 |
Stephenson |
July 8, 2003 |
Physical property determination using surface enhanced raman
emissions
Abstract
A method of and apparatus for determining a physical property of
a material. The method includes: attaching nanoparticles to a
substrate; positioning the substrate near the material;
illuminating the nanoparticles with photons having wavelengths that
stimulate surface enhanced Raman emissions; detecting photons
emitted as a result of the illumination; and determining said
physical property of said material using said detected photons. The
apparatus includes: a substrate; nanoparticles attached to the
substrate; a light source, connected to the substrate, for
illuminating the nanoparticles with photons having wavelengths that
stimulate surface enhanced Raman emissions; a photodetector,
connected to the substrate, for detecting photons emitted as a
result of illumination of the nanoparticles; and a processor,
connected to the photodetector, for determining a property of
material near the nanoparticles from the detected photons. The
inventive method and apparatus are particularly adapted for use in
connection with hydrocarbon exploration and production
activities.
Inventors: |
Stephenson; Kenneth E.
(Newtown, CT) |
Assignee: |
Schlumberger Technology
Corporation (Ridgefield, CT)
|
Family
ID: |
25304558 |
Appl.
No.: |
09/848,892 |
Filed: |
May 4, 2001 |
Current U.S.
Class: |
356/301; 356/307;
356/326 |
Current CPC
Class: |
G01J
3/44 (20130101); G01N 21/658 (20130101) |
Current International
Class: |
G01N
21/65 (20060101); G01N 21/63 (20060101); G01J
3/44 (20060101); G01J 003/44 () |
Field of
Search: |
;356/301,326,307 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Applied Spectroscopy, vol. 34 (1980), pp. 411-414, Dwain E. Diller
et al., "Composition of Mixtures of Natural Gas Components
Determined by Raman Spectrometry". .
Fiber Optic Sensors, (1991), pp. 333-335, ed. Eric Udd. .
http://www-ece.rice.edu/.about.halas/research.html, Apr. 19, 2001,
pp. 1-2, Halas Nanoengineering Group Research. .
Journal Chem. Phys., vol. 111, (1999), pp. 4729-4735, S. J.
Oldenburg, et al., "Surface Enhanced Raman Scattering in the Near
Infrared Using Metal Nanoshell Substrates". .
Journal Opt. Soc. Am., B/vol. 16, No. 10 (1999), pp. 1824-1832,
Richard D. Averitt, et al., "Linear Optical Properties of Gold
Nanoshells". .
Surface Enhanced Raman Scattering, (1982), pp. 109-128, M. Kerker,
et al., "Enhanced Raman Scattering by Molecules Adsorbed at the
Surface Coloidal Particles". .
Topics in Current Physics #11,(1979), "Raman Spectroscopy of Gases
and Liquids" ed. A. Weber..
|
Primary Examiner: Le; Thien M.
Assistant Examiner: Sanders; Allyson N
Attorney, Agent or Firm: Batzer; William B. Ryberg; John
J.
Claims
What is claimed is:
1. A method of determining a physical property of a material, said
method comprising the steps of: attaching nanoparticles to a
substrate; positioning said substrate near said material;
illuminating said nanoparticles with photons having wavelengths
that stimulate surface enhanced Raman emissions; detecting photons
emitted as a result of said illumination; and determining said
physical property of said material using said detected photons.
2. A method according to claim 1, wherein said substrate comprises
an optical fiber.
3. A method according to claim 2, wherein said optical fiber
consists of a fiber core surrounded by a fiber cladding, defining
an interface therebetween, and said particles are located near said
interface.
4. A method according to claim 1, wherein said substrate comprises
porous glass.
5. A method according to claim 1, wherein said material is a
fluid.
6. A method according to claim 1, wherein said material is located
within a wellbore within the earth's subsurface.
7. A method according to claim 1, wherein said physical property is
temperature.
8. A method according to claim 1, wherein said determining a
physical property of said material comprises determining one or
more chemical components of said material.
9. A method according to claim 1, wherein said material includes at
least one of crude oil, natural gas, or water.
10. A method according to claim 1, wherein said substrate is
located within a well logging tool.
11. A method according to claim 1, wherein said substrate is
located beneath the surface of the earth, said nanoparticles are
illuminated by a light source located above the surface of the
earth, and said emitted photons are detected by a photodetector
located above the surface of the earth.
12. An apparatus for determining a physical property of a material
comprising: a substrate; nanoparticles attached to said substrate;
a light source, connected to said substrate, for illuminating said
nanoparticles with photons having wavelengths that stimulate
surface enhanced Raman emissions; a photodetector, connected to
said substrate, for detecting photons emitted as a result of
illumination of said nanoparticles; and a processor, connected to
said photodetector, for determining a physical property of material
near said nanoparticles from photons detected by said
photodetector.
13. An apparatus according to claim 12, wherein said substrate
comprises an optical fiber.
14. An apparatus according to claim 13, wherein said optical fiber
consists of a fiber core surrounded by a fiber cladding, defining
an interface therebetween, and said particles are located near said
interface.
15. An apparatus according to claim 12, wherein said substrate
comprises porous glass.
16. An apparatus according to claim 12, wherein said physical
property is temperature.
17. An apparatus according to claim 12, wherein said determining a
physical property of said material comprises determining one or
more chemical components of said material.
18. An apparatus according to claim 12, wherein said substrate is
attached to a well logging tool.
19. An apparatus according to claim 12, wherein said substrate is
located beneath the surface of the earth, said light source is
located above the surface of the earth, and said photodetector is
located above the surface of the earth.
20. An apparatus according to claim 19, wherein said photons
produced by said light source have wavelengths in the near infrared
spectrum.
21. An apparatus according to claim 12, wherein said substrate is
located within a pipe carrying naturally occurring or processed
hydrocarbons.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a method of and apparatus for
determining a physical property of a material and is particularly
related to a method of and apparatus for determining a physical
property of a material using surface enhanced Raman emissions.
Various methods of and apparatus for determining physical
properties of materials are commonly used in connection with
hydrocarbon exploration and production activities. Optical fibers,
for instance, require no electrical power and are inherently
capable of operating at high temperature. Raman scattering within a
fiber can be used to measure temperature as a function of position
along the fiber and this is the basis of "distributed temperature
sensor" systems. These types of systems are described in Fiber
Optic Sensors, ed. Eric Udd, John Wiley & Sons NY(1991),
incorporated herein by reference. Other types of fiber optic
sensors can be constructed by adding mirrors or diffraction
gratings to the fiber. But, even with these additions, there are
many types of conventional sensors for which no fiber optic
equivalent exists.
Another technology for producing sensors is "micromachining", and
devices produced by this process which involve both mechanical and
electrical components are called MEMS
(Micro-Electro-Mechanical-Systems). These devices typically have
dimensions on the order of 10.sup.-3 m and smallest features on the
order of 10.sup.-6 m. Typically, these devices require electrical
power to operate although some sensors have been produced which are
energized optically. Devices that combine optics and micromachining
are sometimes called MOEMS
(Micro-Opto-Electro-Mechanical-Systems).
For borehole applications, it is often disadvantageous for sensors
to require an electrical power source to operate. MOEMS devices may
require electrical power to operate in addition to the light
provided by the optical fiber. Each such device in the borehole
must have a power supply means. If several MOEMS devices are
distributed along an optical fiber, separate optical connections
are required at each device. Connections are well known to be
sources of failure in borehole equipment and having many such
connections can make a system unreliable. Finally, each MOEMS
device will likely require separate packaging, with ports to allow
optical fiber entry and possibly ports to allow fluid entry. Having
separate MOEMS packages distributed along the optical fiber will
make installation along the well completion time consuming and
difficult.
It is an object of the present invention to provide an improved
method of and apparatus for determining a physical property of a
material, particularly for use in connection with hydrocarbon
exploration and production activities.
SUMMARY OF THE INVENTION
The present invention relates generally to a method of and
apparatus for determining a physical property of a material and
more particularly to a method of and apparatus for determining a
physical property of a material using surface enhanced Raman
emissions. The method includes: attaching nanoparticles to a
substrate; positioning the substrate near the material;
illuminating the nanoparticles with photons having wavelengths that
stimulate surface enhanced Raman emissions; detecting photons
emitted as a result of the illumination; and determining the
physical property of the material using the detected photons. The
apparatus includes: a substrate; nanoparticles attached to the
substrate; a light source, connected to the substrate, for
illuminating the nanoparticles with photons having wavelengths that
stimulate surface enhanced Raman emissions; a photodetector,
connected to the substrate, for detecting photons emitted as a
result of illumination of the nanoparticles; and a processor,
connected to the photodetector, for determining a physical property
of material near the nanoparticles from the detected photons. The
inventive method and apparatus are particularly adapted for use in
connection with hydrocarbon exploration and production activities.
The invention and its benefits will be better understood with
reference to the detailed description below and the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates nanoparticles attached to a porous glass
probe;
FIG. 2 illustrates nanoparticles attached to a fiber optic cable
using porous glass cladding;
FIG. 3 illustrates nanoparticles embedded within a fiber optic
cable near the core/cladding interface;
FIG. 4 illustrates the use of the inventive method and apparatus in
a well logging application; and
FIG. 5 illustrates the use of the inventive method and apparatus in
a hydrocarbon reservoir monitoring application.
DETAILED DESCRIPTION OF THE INVENTION
The inventive method of and apparatus for determining a physical
property of a material utilizes nanoparticles attached to a
substrate. It is desirable to have sensors that are so small they
can be embedded in a substrate, such as an optical fiber. It is
also desirable to be able to extract power directly from the
optical wave in the fiber and to communicate to the surface via the
optical fiber. This is an attraction of nanotechnology.
Nanotechnology is a term used to describe the fabrication,
characteristics, and use of structures ("nanoparticles") with
nanometer dimensions. Nanoparticles are so small that they exhibit
quantum mechanical effects that allow them to interact strongly
with light waves, even though the wavelength of the light may be
much larger than the particle. Nanoparticles are frequently
produced by chemical reactions in solutions. They are quite
different from micro-machined (MEMS) devices, which do not exhibit
quantum effects and are typically produced by lithographic
techniques.
One type of nanoparticle is called a gold nanoshell. These types of
particles are described in more detail in Linear optical properties
of gold nanoshells, R. D. Averitt, et. al., J. Opt. Soc. Am B16
(1999) 1824 and Surface enhanced Raman scattering in the near
infrared using metal nanoshell substrates, S. J. Oldenburg, et.
al., J. Chem. Phys.111 (1999) 4729, both of which are incorporated
herein by reference. Nanoshells are thin (approximately 2 nm thick)
shells of noble metals (for example, gold, silver, or copper)
covering a dielectric sphere (for example, silica or gold sulfide).
All objects with a metal surface, including nanoshells, exhibit a
phenomenon called "surface plasmon resonance" in which incident
light is converted strongly into electron currents at the metal
surface. The oscillating currents produce strong electric fields in
the (non-conducting) ambient medium near the surface of the metal.
The electric fields, in turn, induce electric polarization in the
ambient medium. Electric polarization is well known to cause the
emission of light at wavelengths characteristic of the medium, the
Raman wavelengths. Additional background information regarding this
phenomenon may be found in Surface Enhanced Raman Scattering, ed.
Chang & Furtak, Plenum Press, NY(1982), incorporated herein by
reference. Other types of nanoparticles are known that are capable
of stimulating surface enhanced Raman emissions from nearby
materials, such as gold clusters. In this application, the term
Raman scattering is intended to encompass all related physical
phenomena where the optical wave interacts with the polarizability
of the material, such as Brillouin scattering or polariton
scattering.
Detection and identification of the wavelengths of Raman emission
can be used to "fingerprint" and identify the components of the
ambient medium. The process of stimulating the surface plasmon
resonance with light and subsequent emission of light at Raman
wavelengths is called "surface enhanced Raman scattering" (SERS).
The advantage of nanoshells for SERS is the ability to tune the
wavelength of the surface plasmon resonance to any desired value by
adjusting the thickness of the shell and diameter of the dielectric
sphere. For purposes of this invention, it may be desirable to tune
the resonance to the near infrared, where transmission through
optical fiber glass is possible over long distances with little
absorption and where inexpensive laser sources exist. Nanoshells
may be obtained from The Halas Nanoengineering Group at Rice
University, 6100 Main Street, Houston, Tex. 77005.
SERS has been shown to enhance the intensity of Raman scattering in
material near the surface of the shell by as much as 10.sup.6. In
Surface enhanced Raman scattering in the near infrared using metal
nanoshell substrates, S. J. Oldenburg, et. al., J. Chem. Phys. 111
(1999) 4729, for instance, nanoshells were suspended in a colloidal
solution containing the organic compound p-mercaptoaniline and the
Raman scattering intensity was compared to the same solution
without suspended nanoshells. The p-mercaptoaniline Raman
enhancement in this case was reported to be a factor of
approximately 200,000.
Raman scattering is commonly used in the laboratory as a sensitive
fingerprint of molecular concentration. Raman spectra of natural
gas mixtures and of H.sub.2 S are known, for example, from publicly
available scientific literature. See, for example, Raman
Spectroscopy of Gases and Liquids, ed. A. Weber, Springer-Verlag
Berlin (1979); and Composition of Mixtures of Natural Gas
Components Determined by Raman Spectrometry, D. E. Diller, et. al.,
Appl. Spec. 34 (1980) 411, both of which are incorporated herein by
reference. However, without an enhancement mechanism such as
nanoshells, the low Raman intensity makes these measurements
difficult to implement in a borehole, even though they are of
interest for real-time monitoring of reservoir fluids. One of the
benefits of the present invention is the ability to make such
measurements viable in real-time in a borehole environment.
In an embodiment of this invention, shown schematically in FIG. 1,
nanoparticles are attached to a substrate by embedding gold
nanoshells 12 in a porous glass matrix 14 at the end of an optical
fiber 16. Methods to produce porous glass are well known. For
optimum performance, the index of refraction of the glass is
preferably chosen to be higher than the surrounding material, which
could be, for instance, reservoir fluids in a borehole. In FIG. 1,
incident light 18, from a light source (discussed below) travels
through the fiber core 20, reflecting internally as necessary at
the interface between the fiber core and the fiber cladding 22, to
the porous glass matrix 14. A portion of the incident light 18
passes through the porous glass matrix 14 and is absorbed by the
nanoshells 12. A portion of the material in which the substrate is
positioned, in this example natural gas, has adsorbed onto the
nanoshells 12 and the photons in the incident light 18 stimulates
surface enhanced Raman emissions from this material. A portion of
these emissions return through the optical fiber 16 to a
photodetector and processor which will be discussed in more detail
below. Because the Raman signal from the fluids surrounding the
nanoshells is enhanced, this type of sensor could be used in the
borehole to sense H.sub.2 S in gases and identify components of
natural gases. It could also be used to identify components in
borehole liquids.
While the embodiment shown in FIG. 1 is simple and relatively easy
to construct, it does not produce a distributed measurement. Shown
in FIG. 2 is an embodiment of the inventive method and apparatus
that may be used for this purpose. In this embodiment, short
sections of fiber cladding 22 from the optical fiber 16 are
replaced with porous glass cladding 24 having embedded nanoshells
12. The refractive index of the porous glass cladding 24 is chosen
to be intermediate between the refractive index of the fiber
cladding 22 and the fiber core 20. This ensures that some of the
Raman light emitted by the material near the nanoshells 12 will be
trapped and propagated along the core/cladding waveguide. As the
Raman light emitted from one porous glass region travels through
the core/cladding and reaches another porous glass region, some of
the Raman light may escape through the porous glass section. In
order to avoid excessive loss of Raman light, the total length of
porous glass cladding 24 along the optical fiber 16 will typically
be much less than the length covered by conventional fiber cladding
22.
As discussed above, distributed temperature sensing in optical
fibers by means of Raman backscattering is well known in the art.
This method uses the fact that the ratio of Stokes to anti-Stokes
Raman scattering in the silica of the fiber core is sensitive to
temperature. Optical time domain reflectometry (OTDR) is used to
obtain the temperature as a function of distance (travel time)
along the fiber. One of the primary difficulties with this
measurement is the low intensity of the Raman signal, due to low
quantum mechanical cross-section for Raman scattering. This creates
a low signal-to-noise (S/N) which limits the spatial resolution and
temperature precision. The present invention may be used to
increase the signal to noise ratio of the measurement to give
better resolution and precision. A schematic diagram of this
embodiment is shown in FIG. 3.
In this embodiment, gold nanoshells 12 may be embedded directly
into the fiber core 20 of the optical fiber 16 itself or,
alternatively, at the interface between the fiber core 20 and the
fiber cladding 22. In FIG. 3, the nanoshells 12 are placed at the
interface between the fiber core 20 and the fiber cladding 22. The
nanoshells 12 are tuned (by choosing the appropriate shell
thickness and diameter) to have surface plasmon resonance close to
the wavelength of the incident light 18. The particular choice of
wavelength is a compromise between maximizing the Raman emission 26
and moderating the attenuation of the incident light wave 18 due to
interactions with the nanoshell 12. In other words, the resonance
is chosen to optimize the production of Raman light per unit of
absorption of incident light by the nanoshells 12. This embodiment
demonstrates that it is not necessary for the nanoparticles to be
immediately adjacent to the material being sensed. If the section
of the optical fiber 16 shown in FIG. 3 is placed within borehole
fluids, a physical property (temperature) of a nearby material (the
fluids) may be determined from the stimulated surface enhanced
Raman emissions even though the nanoparticles are not in physical
contact with the borehole fluids.
Other methods for attaching the nanoparticles to the substrate are
possible, such as by using reflectance matching adhesive or by
creating micromachined receptacles for the nanoparticles.
The present method and apparatus may be used, for instance, in a
well logging environment, as shown in FIG. 4. Various methods for
optically analyzing fluids using well logging equipment are known,
such as those methods and apparatus described in commonly-owned
U.S. Pat. Nos. 3,780,575; 3,859,851; 4,994,671; 5,167,149;
5,166,747; 5,201,220; 5,266,800; 5,331,156; 5,859,430; 5,939,717;
and 6,023,340; each of which is incorporated herein by reference.
In the embodiment shown in FIG. 4, for instance, a borehole logging
tool 30 is shown for testing earth formations and analyzing the
composition of fluids from the formation 32. The tool 30 is
suspended in the borehole 34 from the lower end of a typical
multi-conductor cable 36 that is spooled in the usual fashion on a
suitable winch (not shown) on the surface. On the surface, the
cable 36 is electrically connected to an electrical control system
38. The tool 30 includes an elongated body 40 which encloses the
downhole portion of the tool control system 42. The elongated body
40 also carries a selectively extendible fluid admitting assembly
44 and a selectively extendible tool anchoring member 46 which are
respectively arranged on opposite sides of the body. The fluid
admitting assembly 44 is equipped for selectively sealing off or
isolating selected portions of the wall of the borehole 34 such
that pressure or fluid communication with the adjacent earth
formation is established. Also included with tool 30 is a fluid
analysis module 48 through which the obtained fluid flows. The
fluid may thereafter be expelled through a port (not shown) or it
may be sent to one or more fluid collecting chambers 50 and 52
which may receive and retain the fluids obtained from the
formation. Control of the fluid admitting assembly 44, the fluid
analysis module 48, and the flow path to the collecting chambers is
maintained by the electrical control systems 38 and 42. The fluid
analysis module 48 may contain, for instance, a porous glass probe
having attached nanoparticles as shown in FIG. 1. By tuning the
resonance of the nanoparticles to the wavelength of the light
source or by adjusting the wavelength of the light source to match
the resonant frequency of the nanoparticles, surface enhanced Raman
emissions may be stimulated in the fluid and one or more physical
properties of the fluid may be determined.
The present method and apparatus may also be used in a permanent
hydrocarbon reservoir monitoring environment, as shown in FIG. 5.
In FIG. 5, an uphole light source 60 is shown, which may produce a
high amplitude near infrared signal at selected wavelengths (such
as an Argon ion laser). Also shown in FIG. 5 are an uphole
photodetector 62 (such as a spectrometer) and a processor 64 for
processing signals received from the photodetector. Optical fibers
66 and a directional coupler 68 are used to connect the uphole
light source 60 and the uphole photodetector 62 to a plurality of
sensor sections 70 located at various locations of the wellbore 72.
The optical fibers 66 are preferably run through a small diameter
conduit 74 that is cemented in the annulus 76 surrounding the
wellbore 72. Alternatively, the conduit 74 may be run inside the
wellbore or production tubing. The sensor sections 70 may consist
of the components illustrated schematically in FIGS. 1, 2, or 3.
When a physical property of the borehole fluid 78 is intended to be
determined, the nanoparticles within the sensor sections 70 must be
sufficiently near the borehole fluid to allow the desired physical
property to be determined from the stimulated surface enhanced
Raman emissions. Components disclosed in commonly-assigned
co-pending U.S. patent application Ser. No. 09/604,440, entitled
"Permanent Optical Sensor Downhole Fluid Analysis Systems" and
filed Jun. 26, 2000, incorporated herein by reference, may be used
in the inventive method and apparatus. The components of the
relatively simple sensor section 70 are particularly well adapted
for the high temperature/high pressure conditions typically found
in hydrocarbon exploration and production environments.
The foregoing descriptions of preferred and alternate embodiments
of the present invention have been presented for purposes of
illustration and description. They are not intended to be
exhaustive or to limit the invention to the precise examples
described. Many modifications and variations will be apparent to
those skilled in the art. These embodiments were chosen and
described in order to best explain the principles of the invention
and its practical application, thereby enabling others skilled in
the art to understand the invention for various embodiments and
with various modifications as are suited to the particular use
contemplated. It is intended that the scope of the invention be
defined by the accompanying claims and their equivalents.
* * * * *
References